This invention relates to an electronic circuit for controlling the supply voltage of electromagnets, electric motors, resistors, in single- and three-phase systems without making use of auxiliary power inputs.
Several circuits have been proposed and are available commercially which enable the voltage applied to a load, such as electromagnets, motors, resistors, to be controlled in single- and three-phase systems; in a type of these circuits, additionally to the load power supply proper, either auxiliary power inputs or auxiliary drive circuits for the control circuit must be provided in order to obtain a precise adjusting of the load voltage.
In another type, on the other hand, generally of the phase shifting class using RC networks, the control power is directly supplied by the load power supply, thereby the circuitry is a comparatively simple one with respect to the first type; however the adjusting is scarcely accurate, mainly with respect to the maximum and minimum RMS load voltage.
Such prior circuits, regardless of their actual construction, have all the disadvantage of being both expensive and complicated.